If you made even a passing attempt at understanding this space you would see how wrong you are.

Anyone can interact with a contract directly, you don't need any FE or BE at all.

I can't speak to the specifics of dydx since I am not a user and haven't done my due diligence on them, but with every other dex I have ever interacted with it is entirely possible to use their service entirely from the contract interface.

Its usually the first thing I do to ensure that I can access my funds without any external dependencies.